【iOS】淺拷貝和深拷貝
阿新 • • 發佈:2018-06-14
簡單 HR 除了 深淺拷貝 感謝 with 分配 指針 object
淺拷貝和深拷貝
- 淺拷貝即指針拷貝,可以認為是給一只狗加了一條繩子;深拷貝不但拷貝了對象的指針,還在系統中在分配了一塊內存用來存放拷貝對象的內容,可以認為是產生了一條帶繩子的新狗。即淺拷貝是兩根繩子一條狗,深拷貝是兩根繩子兩條狗且每只狗對應各自的繩子。
- 圖示:
深淺拷貝取決於拷貝後的對象是不是和被拷貝對象的地址相同,如果不同,則產生了新的對象,即為深拷貝。如果不同,則只是指針拷貝,相當於retain一次原對象,即為淺拷貝。
copy與mutableCopy
copy復制後的對象是不可變對象,mutableCopy復制後的對象是可變對象,與原始對象是否可變無關。
非集合類的copy與mutableCopy
- 對不可變對象執行copy操作,是指針復制(淺拷貝),執行mutableCopy操作是內容復制(深拷貝)。
- 對可變對象執行copy操作和mutableCopy操作都是內容復制(深拷貝)。
代碼表示如下:
[immutableObject copy]; // 淺復制 [immutableObject mutableCopy]; // 深復制 [mutableObject copy]; // 深復制 [mutableObject mutableCopy] ; // 深復制
容器類的淺復制和深復制
- 容器對象和非容器對象類似,可變對象復制的都是一個新對象,不可變對象copy的是淺復制,mutableCopy是深復制
- 對於容器而言,元素對象始終是指針復制。
驗證代碼:
NSMutableArray *array01 = [NSMutableArray arrayWithObjects:@"a",@"b",@"c", nil]; NSArray *copyArray01 = [array01 copy]; NSMutableArray *mutableCopyArray01 = [array01 mutableCopy]; NSLog(@"array01 = %p,copyArray01 = %p",array01,copyArray01); NSLog(@"array01 = %p,mutableCopyArray01 = %p",array01,mutableCopyArray01); NSLog(@"=================================================================="); [array01 addObject:@"d"]; NSLog(@"array01 = %p,copyArray01 = %p",array01,copyArray01); NSLog(@"array01 = %p,mutableCopyArray01 = %p",array01,mutableCopyArray01); NSLog(@"array01 =%@\n copyArray01 =%@\n mutableCopyArray01 =%@",array01,copyArray01,mutableCopyArray01); NSLog(@"array01[0] = %p,array01[1] = %p,array01[2] = %p,array01[3] = %p",array01[0],array01[1],array01[2],array01[3]); NSLog(@"copyArray01[0] = %p,copyArray01[1] = %p,copyArray01[2] = %p",copyArray01[0],copyArray01[1],copyArray01[2]); NSLog(@"mutableCopyArray01[0] = %p,mutableCopyArray01[1] = %p,mutableCopyArray01[2] = %p",mutableCopyArray01[0],mutableCopyArray01[1],mutableCopyArray01[2]); NSLog(@"=================================================================="); [mutableCopyArray01 addObject:@"e"]; NSLog(@"array01 = %p,copyArray01 = %p",array01,copyArray01); NSLog(@"array01 = %p,mutableCopyArray01 = %p",array01,mutableCopyArray01); NSLog(@"array01 =%@\n copyArray01 =%@\n mutableCopyArray01 =%@",array01,copyArray01,mutableCopyArray01); NSLog(@"array01[0] = %p,array01[1] = %p,array01[2] = %p",array01[0],array01[1],array01[2]); NSLog(@"copyArray01[0] = %p,copyArray01[1] = %p,copyArray01[2] = %p",copyArray01[0],copyArray01[1],copyArray01[2]); NSLog(@"mutableCopyArray01[0] = %p,mutableCopyArray01[1] = %p,mutableCopyArray01[2] = %p,mutableCopyArray01[3] = %p",mutableCopyArray01[0],mutableCopyArray01[1],mutableCopyArray01[2],mutableCopyArray01[3]);
打印結果:
2018-06-14 11:16:43.117758+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,copyArray01 = 0x604000443bd0 2018-06-14 11:16:43.117887+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,mutableCopyArray01 = 0x604000443a80 2018-06-14 11:16:43.118014+0800 copy_demo[1988:95724] ================================================================== 2018-06-14 11:16:43.118108+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,copyArray01 = 0x604000443bd0 2018-06-14 11:16:43.118323+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,mutableCopyArray01 = 0x604000443a80 2018-06-14 11:16:43.118485+0800 copy_demo[1988:95724] array01 =( a, b, c, d ) copyArray01 =( a, b, c ) mutableCopyArray01 =( a, b, c ) 2018-06-14 11:16:43.118559+0800 copy_demo[1988:95724] array01[0] = 0x10bf06128,array01[1] = 0x10bf06148,array01[2] = 0x10bf06168,array01[3] = 0x10bf061e8 2018-06-14 11:16:43.118661+0800 copy_demo[1988:95724] copyArray01[0] = 0x10bf06128,copyArray01[1] = 0x10bf06148,copyArray01[2] = 0x10bf06168 2018-06-14 11:16:43.118758+0800 copy_demo[1988:95724] mutableCopyArray01[0] = 0x10bf06128,mutableCopyArray01[1] = 0x10bf06148,mutableCopyArray01[2] = 0x10bf06168 2018-06-14 11:16:43.118891+0800 copy_demo[1988:95724] ================================================================== 2018-06-14 11:16:43.119034+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,copyArray01 = 0x604000443bd0 2018-06-14 11:16:43.119095+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,mutableCopyArray01 = 0x604000443a80 2018-06-14 11:16:43.119185+0800 copy_demo[1988:95724] array01 =( a, b, c, d ) copyArray01 =( a, b, c ) mutableCopyArray01 =( a, b, c, e ) 2018-06-14 11:16:43.119346+0800 copy_demo[1988:95724] array01[0] = 0x10bf06128,array01[1] = 0x10bf06148,array01[2] = 0x10bf06168 2018-06-14 11:16:43.119527+0800 copy_demo[1988:95724] copyArray01[0] = 0x10bf06128,copyArray01[1] = 0x10bf06148,copyArray01[2] = 0x10bf06168 2018-06-14 11:16:43.119595+0800 copy_demo[1988:95724] mutableCopyArray01[0] = 0x10bf06128,mutableCopyArray01[1] = 0x10bf06148,mutableCopyArray01[2] = 0x10bf06168,mutableCopyArray01[3] = 0x10bf06288
深拷貝淺拷貝面試中也經常問到,這只是一個簡單的理解和總結,除了這些,還有很多比較復雜的以及自定義對象的深復制和淺復制。
推薦一篇講得比較詳細和深刻的文章:https://github.com/pro648/tips/wiki/%E6%B7%B1%E5%A4%8D%E5%88%B6%E3%80%81%E6%B5%85%E5%A4%8D%E5%88%B6%E3%80%81copy%E3%80%81mutableCopy。我在整理這篇文章的時候也參考了這篇文章,感謝作者的分享。
【iOS】淺拷貝和深拷貝